The long-term objectives of this proposal are to understand the neurobiological basis of complex cognitive, perceptual and motor processes from the standpoint of neurophysiological and neuroanatomical specializations of the left and right cerebral hemispheres. The aims are to evaluate neural systems involved in the expression of communicative behaviors, execution and perception of motor actions and social behaviors that are hypothesized to be homologs to the evolution of complex human cognition including expressive and receptive language. Positron emission tomography (PET) will be used to assess the neurobiology of gestural and vocal communication in chimpanzees. Additional PET studies will be conducted to evaluate whether the "mirror-neuron" system of motor action and perception previously described in monkeys underlies the execution and perception of complex motor processes, such as imitation, in chimpanzees. PET studies will also be used to evaluate evolutionary hypotheses of language origins that are rooted in the social functions of language. Of specific interest is the link between the evolution of language and the function of social grooming in primates. To test these hypotheses, PET will be used to evaluate the neural systems involved in grooming by chimpanzees. The neurobiology of handedness, one of the most pronounced manifestations of hemispheric specialization, will also be evaluated in the proposed studies. PET will be used to assess where the hand is represented in the primary motor cortex in chimpanzees and these data will be mapped to known neuroanatomical landmarks on the motor strip of chimpanzees. Hand regions will then be mapped and quantifed in the left and right cerebral hemispheres from magnetic resonance images (MRI) and asymmetries in this region will be correlated with various measures of hand preference and skill. The overall studies will contribute to our understanding of factors that influence individual and species differences in the expression of hemispheric specialization.